The present invention relates to a machine for grinding ophthalmic glasses.
The invention is for example applicable to a machine for grinding ophthalmic glasses of the type comprising a stand, a carriage, for example generally U-shaped, mounted on a first shaft so as to be pivotable relative to the stand, a second shaft parallel to the first shaft and comprising at least one grinding wheel driven in rotation by an electric motor, the carriage carrying a clamping shaft parallel to the first shaft and made in two parts between which a glass blank to be ground is held and also driven in rotation for the grinding operations.
The machine comprises for this purpose clamping means which exert an axial force on at least one of the two parts of the clamping shaft and which comprise for this purpose at least one motor-speed reducer unit comprising a motor and means for transmitting the driving force of the motor arranged in a housing.
The output of the motor-speed reducer unit is for example connected to a gear pinion for driving a rack formed on a clamping rod which exerts an axial force on one of the two parts of the clamping shaft.
The glass blank is clamped by supplying the electric motor of the motor-speed reducer unit with power so that it provides a driving force, i.e. a driving torque, which is converted into an axial clamping force by the motor-speed reducer unit and the rack and pinion device.
It has been found that, in the course of utilization of the machine with consequent wear of its component parts, the efficiency of the assembly comprising the motor-speed reducer unit and the rack and pinion device varies, with the result that variations in the clamping force may be particularly high, for example on the order of 30%.
In known machines for grinding ophthalmic glasses, it is consequently not possible to reliably and durably control the value of the clamping force on the glass blank to be ground.